Typical Magnetic Random Access Memory (MRAM) structures have a nonmagnetic layer sandwiched between two ferromagnetic films. The two ferromagnetic films are also known as magnetic thin films. The MRAM employs the magneto resistive properties of this structure to store data. In each storage element, an MRAM employs two lines, commonly termed a word line and a sense string, in order to detect the magnetization direction of these magnetic thin films. Each string comprises a magnetic thin film that serves as a memory element, and the word line generally addresses multiple sense strings. Magnetic thin films that have a parallel moment have a low resistance and are typically assigned the ‘1’ state. Magnetic thin films having an anti-parallel moment have a high resistance and are typically assigned the ‘0’ state, but may also be assigned to the ‘1’ state.
During a read operation, a word current passes through the word line causing the magnetic layers in the sense string to rotate, thereby changing the resistance in the sense string. A sense current passes through the sense string. A sense line receives the signal from the sense string. A differential amplifier compares the signal from the sense line to a reference line to determine whether a one resistance or a zero resistance is stored in the MRAM. A differential amplifier notes the change in voltage across the sense line to determine resistive state of a storage element.
MRAM word lines have relatively large capacitances; carry large currents and switch in a short time period. During operation, an MRAM requires stable voltage changes when switching highly capacitive high current word lines. If stability is not achieved, then undesirable current surges may adversely affect memory operations causing an unstable read and write cycle. When the word line switch is activated, an undesired current pulse may be generated. This could have the result of creating a false or unexpected write to the memory cell being selected.
Other workers have devised solutions that involve using decoding schemes that do not address the need for smooth and stable changes to word line signals. They ignore these changes and all switching control is attempted with the controlling logic circuitry.
Therefore, there is a need to equalize voltage on either side of the word decode circuit prior to the start of a read or write cycle.
There is a further need to reduce undesirable current surges on the word lines.
There is a further need to provide greater control of the read and write current and the associated read and write magnetic fields.
There is a further need to provide a more stable read and write cycle.